Orthodontic management of the developing dentition

The first primary deciduous teeth emerge during infancy around 6 months of age, and following many dynamic stages of dental development and facial growth, the final second-ary permanent

Orthodontic

Management of the Developing Dentition

Martyn T Cobourne

Editor

An Evidence-Based Guide

123

Orthodontic Management of the Developing Dentition

Martyn T Cobourne

Department of Orthodontics

Centre for Craniofacial Development and Regeneration

King’s College London Dental Institute

London

United Kingdom

ISBN 978-3-319-54635-3 ISBN 978-3-319-54637-7 (eBook)

DOI 10.1007/978-3-319-54637-7

Library of Congress Control Number: 2017947876

© Springer International Publishing AG 2017

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Preface

Management of the developing dentition has always been a fundamental role of the orthodontist The transition from primary to secondary dentition is characterised by variation rather than conformity, and a multitude of local and more general prob-lems can manifest during this period of development However, in an era of evidence- based medicine, there is a surprising paucity of high-quality data to help inform decisions that often need to be made during this stage of development.This textbook provides a rich source of information on the many aspects of den-tal development that an orthodontist might be engaged with The text begins with an overview of the normal development of the dentition and the management of early space loss, including enforced extraction of first permanent molars It then covers local problems associated with the mixed dentition, including tooth agenesis and supernumerary teeth, dental trauma and impacted teeth, including maxillary inci-sors and canines Further chapters cover the interceptive management of class II and class III discrepancies and problems associated with the transverse dimension.The chapters have been written by an international group of authors who have considerable expertise in the management of malocclusion and, in many cases, first- hand experience of conducting high-quality clinical trials investigating treatment interventions for these problems The title of the book proclaims that it is evidence- based and in some areas it is In particular, there have been recent advances in our knowledge of best practice for managing impacted maxillary canines and both class

II and class III malocclusions However, there are many common clinical problems that affect the developing dentition, which currently have only anecdote and retro-spective clinician experience to inform them Much work needs to be done in inves-tigating many of these interventions with appropriate methodology In the meantime, this textbook will provide you with the best current evidence that there is

1 Development of the Dentition 1

Maisa Seppala and Martyn T Cobourne

2 Space Loss and Crowding 21

Anthony J Ireland, Fraser McDonald, Rebecca John,

and Jonathan R Sandy

3 First Permanent Molars 33

Gavin J Mack

4 Supernumerary Teeth 53

Helen Tippett and Martyn T Cobourne

5 Tooth Agenesis 67

Sirpa Arte, Wael Awadh, Pekka Nieminen, and David P Rice

6 Trauma to the Permanent Maxillary Incisors in the Mixed

Dentition and Orthodontics 85

Jadbinder Seehra and Serpil Djemal

7 Impacted Maxillary Central Incisors 109

Shruti Patel

8 Early Management of the Palatally Displaced Maxillary

Permanent Canine 131

Philip E Benson and Nicola A Parkin

9 Early Treatment of Class II Malocclusion 151

Andrew DiBiase and Paul Jonathan Sandler

10 Class III Malocclusion 169

Simon J Littlewood

11 Early Management of Posterior Crossbites 185

Jayne E Harrison

Contents

© Springer International Publishing AG 2017

M.T Cobourne (ed.), Orthodontic Management of the Developing Dentition,

DOI 10.1007/978-3-319-54637-7_1

M Seppala • M.T Cobourne ( * )

Department of Orthodontics, Craniofacial Development and Stem Cell Biology,

King’s College London Dental Institute, London SE1 9RT, UK

e-mail: martyn.cobourne@kcl.ac.uk

1

Development of the Dentition

Maisa Seppala and Martyn T Cobourne

Abstract

Respiration, swallowing, speech and mastication are the primary roles of the oral cavity The human dentition has evolved to effectively carry out the latter func-tion by having teeth with different sizes and shapes and by going through a tran-sition from primary to secondary dentitions that ensure optimal space and occlusal relationships in the adult Teeth start forming early during the sixth week of embryonic development and are governed by molecular signals that ensure the right teeth develop at the right time in the right place The first primary (deciduous) teeth emerge during infancy around 6 months of age, and following many dynamic stages of dental development and facial growth, the final second-ary (permanent) third molar teeth erupt around the age of 19 years to complete the permanent dentition However, even after this event, occlusal changes con-tinue to take place through late-stage facial growth, alveolar development, post- emergent eruption and occlusal forces

Development of the Dentition

The human dentition begins formation in the embryo with postnatal development characterised by the transition from deciduous to permanent dentitions The decidu-ous dentition consists of two incisors, one canine and two molars in each dental quadrant, whilst the permanent dentition consists of the successional incisors, canines and premolars and accessional molars (Fig 1.1)

Embryonic Dental Development

The first 3 months of embryonic development are crucial for formation of the facial structures that derive from five fundamental processes: the paired mandibular, paired maxillary and frontonasal processes [1] The oral surfaces of these processes provide the platform for dental development as the lower dentition derives from tis-sue components originating in the mandibular processes and the upper incisors as well as the rest of the maxillary teeth develop within the frontonasal and maxillary processes, respectively The appearance of the horseshoe-shaped epithelial thicken-ings that form in the early oral cavity around 6 weeks of gestation marks the start of dental development Subsequently, this continuous epithelial band divides into an outer vestibular and inner dental lamina, the former giving rise to the lip and cheek vestibules and the latter to the enamel organs of the teeth [2 3]

Molecular Basis of Dental Development in Brief

Teeth are epithelial appendages like hair, sweat glands and nails and share many lar morphological and molecular stages during their development Their growth relies

simi-on epithelial-mesenchymal interactisimi-ons mediated by secreted signalling molecules that, in turn, induce expression of multiple transcription factors These signals are repeatedly used at different stages of dental development, and after first establishing oral-aboral and mesiodistal polarity in the jaws, then continue to regulate initiation, growth, morphogenesis, cell differentiation and cusp patterning of the teeth [4 6].Humans are heterodonts, who have teeth with different sizes and shapes including two incisors, one canine, two premolars and three molars in each dental quadrant The current developmental model for investigating tooth development is the mouse, which has a reduced dentition in comparison to humans However, there is much commonal-ity in the fundamental mechanisms underlying tooth development in mouse and human due to their genomic similarity and comparable stages of dental development [7]

In mice, teeth with different morphology develop depending on their mesiodistal position in either of the jaws, and the heterodont patterning is under control of at least

Fig 1.1 The human dentition forms as a transition from deciduous to permanent dentition The deciduous dentition consists of two incisors, one canine and two molars in each dental quadrant

(a), whilst adult jaws accommodate an additional two premolars between the canine and first molar

as well as a third molar (b)

two well-studied signalling molecules, bone morphogenetic protein 4 (Bmp4) and blast growth factor 8 (Fgf8) expressed by the oral epithelium Bmp4 specifies the incisor

fibro-region by inducing expression of homeobox-containing transcription factors Msh

homeobox 1 (Msx1) and 2 (Msx2) in the underlying mesenchyme and in the molar field through Fgf8 initiating expression of BarH-like homeobox 1 (Barx1) and Distal-less 2 (Dlx2) [8, ] Significantly, murine studies have shown that inhibition of Bmp4 results

in ectopic expression of Barx1 in the presumptive incisor region, which can cause

trans-formation of the incisors into teeth with more molariform characteristics, highlighting the importance of these homeobox genes in regulating heterodont patterning [9

After mesiodistal polarity has been established, two signalling molecules, sonic hedgehog (Shh) and Wnt7b, become reciprocally expressed in the oral epithelium

Interestingly, the expression domain of Shh corresponds to the tooth-forming region and Wnt7b to the non-tooth-forming oral epithelium Subsequently, their roles have

been shown to delineate the regions that have potential for tooth formation [10] At the time when tooth formation is initiated, Fgf8 also provides an inductive signal for formation of the localised thickenings in the oral epithelium that give rise to dental placodes Fgf8 continues to induce proliferation in the dental placodes and together with Shh controls early cellular morphogenetic changes that result in progression of tooth development from a thickening to bud stage [11] Following this early pattern-ing, a whole host of molecules become dynamically expressed and take part in com-munication between the oral epithelium and underlying mesenchyme to ensure normal progression of dental development

Histological Basis of Dental Development in Brief

The different stages of dental development are named after their resemblance to the shape of the invaginating epithelium that progress from thickening to bud, cap, bell and late bell stages The surrounding mesenchyme condenses around the invaginat-ing epithelium and at cap stage becomes partly encapsulated At the bell stage, the enamel knots at the tip of the future cusps become visible These are signalling centres that are important for morphogenesis and required for normal cusp forma-tion in molars At the late bell stage, histodifferentiation begins and derivatives of the oral ectoderm give rise to enamel-producing ameloblasts, whilst the rest of the tooth originates from cranial neural crest-derived mesenchyme, including dentin- producing odontoblasts, cementum-producing cementoblasts, periodontal liga-ments and pulpal tissue [3 4 6] Calcification of the deciduous dentition begins around 3–4 months of embryonic development [3 12]

As diphyodonts, humans have two generations of teeth Preparation for the sition from primary to secondary dentition begins during prenatal life Successional secondary teeth develop from localised lingual proliferations from the dental lamina

tran-of their corresponding primary predecessors and give rise to two incisors, canine and two premolars in each dental quadrant The rest of the secondary dentition are accessional teeth that include all three molars that form from a backward extension

of the distal aspect of the primary second molar The first sign of successional tooth development is seen around 3–4 months, whilst the accessional teeth start to form around 5 months of embryonic development [3] (Fig 1.2)

Postnatal Development of the Dentition (Box 1.1)

At birth the head is nearly half of the body mass, and the mandible is strikingly small and retrognathic in relation to the maxilla [2] The upper lip is short and the lower lip forms the majority of the anterior seal Even when dental development has begun already early on during prenatal life, the infant’s first smile is predominated

by the presence of edentulous gum pads However, inside the developing alveolar processes, dental development is well underway as the deciduous central incisor crowns have almost fully calcified, and the rest of the deciduous dentition has also begun this process

p

pt

st

Fig 1.2 Late cap stage tooth germ: developing mandibular incisor (a) and mandibular canine (b)

During human embryonic development, the dental lamina (dl) connects the cap stage tooth germ

to the oral epithelium Outer enamel epithelium (oee) and inner enamel epithelium (iee) derive from the invaginated oral epithelium, and the iee gives rise to enamel-producing ameloblasts Encapsulated neural crest-derived mesenchymal cells adjacent to the iee receive signals from the iee and differentiate into dentin-producing odontoblasts Pulpal tissue (p) also originates from the

mesenchyme Sr stellate reticulum (a) The successional permanent tooth (st) is beginning to

develop on the lingual side of the bud stage primary tooth (pt), and these are linked together by the

successional lamina (arrow) (b)

The First 6 Months

In the newborn maxilla, the horseshoe-shaped gum pad surrounds the shallow ate and overlaps the U-shaped mandibular gum pad The future positions of the developing teeth can be seen on the gum pads as small segmented elevations sepa-rated by small transverse grooves (Fig 1.3) One of these grooves, the ‘lateral sul-cus’, is prominent, extending vertically to the buccaneers sulcus and corresponding

pal-to the distal side of the future deciduous canine The second molars are the last deciduous teeth to start developing, and subsequently the elevations in the prospec-tive second molar regions do not become evident until around 5 months of age Just palatal or lingual to these elevations, a dental groove represents a structure that is a remnant of the invaginated epithelial organs of the developing teeth In addition, in the maxilla another shallow groove, the gingival groove, is located more palatally and anatomically separates the alveolar and palatal epithelium apart from each other [2 3]

At birth, some of the infant’s vital physiological functions need to change abruptly, and the time of adaptation to a new environment can be associated with disruptions in enamel calcification resulting in formation of the so-called neonatal line Normally this horizontal line is not visible by eye, but following more stressful

or complicated births, it can become noticeable [13], and its location depends on the developmental stage of the relevant tooth crown at the time of birth Although most

Fig 1.3 Profile view of a 3-week-old baby boy and oral view of the maxilla Newborn children

have a small mandible in comparison to the maxilla (a), and their edentulous gum pads have small segmented elevations that mark the sites of the developing teeth (b)

Box 1.1 Key Stages of Development of the Deciduous Dentition

– 6 weeks of gestation: development of the deciduous dentition begins

– 6 months: first deciduous teeth, mandibular central incisors, erupt

– 2½ years: all 20 deciduous teeth have erupted

– Root development of deciduous dentition is completed within 12–18 months after their eruption to oral cavity

– Teeth normally erupt within a few weeks from eruption of the teeth in the contralateral side of the same jaw

newborns are edentulous, 1:1000 to 1:30,000 depending on the racial group have natal teeth at birth or neonatal teeth that erupt within 30 days after birth These are most frequently seen in the mandibular incisor region and can be either supernumer-ary or prematurely erupted deciduous teeth It is difficult at this stage to determine

if they are part of the normal complement of the deciduous dentition, and thereafter the decision on their removal depends on the presence of any possible symptoms such as disrupted feeding that can cause inadequate nutrient intake, ulcerations or increased mobility with risk of aspiration [14]

Infants get their nutrition up to the first 3–6 months exclusively from breast or substitute milk, and their ability to thrive depends on establishment of a successful feeding pattern In the newborn, the tongue normally sits between the maxilla and mandible and during suckling forms a seal against the lower lip Coordinated move-ments of the tongue, lips and cheeks during suckling activate the facial muscles and are considered to be important in stimulating facial growth [15] During the first year, significant transverse growth takes place in both maxillary and mandibular sutures providing approximately 2 mm more space for eruption of the deciduous incisors [16]

From 6 Months to 5 Years of Age

The first deciduous teeth erupt around the same time as the infant adapts to a more complex swallowing pattern and is physiologically ready for weaning [17] Teething can be a big event in the infant’s life, as their eruption can cause multiple relatively minor symptoms such as general irritability, disturbed sleep, an increase in body temperature, drooling, gum-rubbing and increased biting [18]

The first deciduous teeth to emerge are the lower central incisors (median age 6.8 months), and contralateral teeth normally erupt only a few weeks apart from each other Although some variation does take place in the eruption pattern, typically every following few months, a new pair of incisors erupts in the following sequence: maxillary central incisors (9.1 months), lateral maxillary incisors (9.8 months) and lower lateral incisor (11.4 months) [19] By the end of the first year of life, around two thirds of deciduous incisor root development is completed Variable degrees of root formation are also evident in the rest of the developing deciduous dentition excluding the second molars that are just completing their crown formation [12].After a short while, eruption of the deciduous teeth resumes with eruption of the first molars (maxillary 14.8 and mandibular 15.4 months) slightly before the canines (maxillary 17.6 and mandibular 18.0 months) The last deciduous teeth to erupt are the second deciduous molars (mandibular at 26.2 months, maxillary at 26.6 months), following which, the full complement of five deciduous teeth is present in each dental quadrant [19] Root development of the primary dentition is completed approximately 12–18 months after their eruption, and subsequently all deciduous incisors complete their root development by age of 2 years, first molars 2½ years and second molars 3 years, and deciduous canines are the last ones to complete their root development around 3¼ years of age [12]

Eruption sequence of the primary dentition is more important than chronological timing Large variation in eruption times exists, and it is not unusual that some of the children do not get their first teeth until the age of one (Table 1.1) As a general rule, 6-month deviation from the average eruption times is considered normal If a child at the age of 3 years has not yet attended any dental appointments, this is now

a good time to visit dentist or dental hygienist in order to confirm normal dental development and good dental health The primary dentition is usually established

by the age of 3 years (Fig 1.4)

Space and Occlusal Development in the Primary Dentition

From birth to 2 years of age, the intercanine width increases around 3.5 mm in the mandible and 5 mm in the maxilla [20] Subsequently, even the primary incisors might erupt in crowded positions, transverse growth ideally results in spacing in the labial segments providing additional space for the wider permanent incisors to erupt In addition to generalised upper and lower incisor spacing, ‘primate spaces’ mesial to the upper canines and distal to the lower canines provide further space for permanent dentition and are the most prevalent feature of the primary dentition [21].Deciduous incisors are typically more upright, and the overbite tends to be tran-siently deep in the early deciduous dentition Overbite reduces as a result of increase

in the posterior lower facial height that is anteriorly compensated by post-emergent eruption and augmentation of the alveolar bone Both jaws also grow in an

Table 1.1 Deciduous dentition: median eruption times

Deciduous C incisor L incisor Canine First molar

Second molar Maxilla (months)

Median 9.1 9.8 17.6 14.8 26.6

In brackets 5 and 95%

percentiles

(6.8–12.7) (7.2–15) (13.6–23.8) (11.8–18.5) (20.1–34.4) Mandible (months) 6.8

(4.3–10.6)

11.4 (7.9–16.7)

18.0 (14.0–24.6)

15.4 (11.8–18.8)

26.2 (20.2–33.1) According to Nyström [ 19 ]

Fig 1.4 Primary dentition Complete primary dentition of a 3-year-old girl with the presence of

primary spaces mesial to the maxillary canines and distal to the lower canines (a, b)

anterior- posterior direction, and, significantly, the mandible grows faster than the maxilla, resulting in more optimal jaw relationships, reduction in overjet and erup-tion of the teeth in better occlusion [2 22] Molar length increases with its highest rate up to the age of 3 years, providing posteriorly more space for eruption of the rest of the primary dentition [20] In the deciduous dentition, the most common molar relationship is edge to edge, and the tendency for Class II malocclusion is much more common than Class III [21].

Development of the Permanent Dentition (Box 1.2)

Transition from deciduous dentition to permanent dentition is divided into two stages, early and late mixed dentition, as permanent teeth erupt in groups These two stages of rapid dental development are separated by around a year and a half of more silent period of time, when no further deciduous teeth exfoliate, but progression of dental development can be assessed from radiographs based on the amount of crown and root development as well as the presence of root resorption in the deciduous dentition

Transition to the permanent dentition commonly begins around the same time with the start of the juvenile growth spurt, at around 6–7 years of age, as the mandibular central incisors (6–7 years) or first molars (5.5–7 years) erupt Only another year later, the mandibular lateral incisors (7–8 years) erupt around the same time with the

Box 1.2 Key Stages of Development of the Permanent Dentition

– 14 weeks of embryonic development: development of the permanent tion begins

denti-– 6 years: first permanent teeth, mandibular central incisors or first molars, erupt

– 9–10 years: permanent maxillary canines palpable bilaterally in the buccal sulcus

– 11 years: permanent maxillary canines erupt

– 12 years: permanent second molars erupt and complete development of the permanent dentition (excluding third molars)

– 19 years: if present, permanent third molars erupt; however, their timing has a lot of variation depending on the space availability

– Root development of the permanent dentition completed within 2–3 years after their eruption to oral cavity

– Eruption within 2 years from average eruption time is considered as mal variation

nor-– Teeth normally erupt within half a year from eruption of the teeth in the contralateral side of the same jaw

upper central incisors (7–8 years) Lastly, the early mixed dentition stage is complete

as the upper lateral incisors erupt at approximately 8–9 years of age [12] As the deciduous teeth exfoliate, the permanent successors are expected to erupt within the following 6 months The same time frame is applied when a permanent tooth has erupted on one side; the contralateral deciduous tooth can be expected to be lost again within the following 6 months Similarly to the deciduous dentition, the correlation between chronological and dental age is also poor in the permanent dentition, and up

to 2 year deviations from average eruption times are considered normal

As the upper central incisors erupt, they can be flared distally leaving a space in the midline This midline diastema can be present due to crowding inside the anterior maxillary bone where the unerupted lateral incisor crowns are still in their vertical

c

Fig 1.5 Early mixed dentition Transition to early mixed dentition usually begins around 6–7

years of age (a) Teeth exfoliate following root resorption of the deciduous teeth and after atraumatic loss good healing of the gingival tissue can already be seen a few hours after exfoliation (b, c)

Others

– Eruption sequence in both deciduous and permanent dentition is more important than correlation between eruption times and chronological age.– Females are typically ahead of their male counterparts in terms of their dental development

position high and can apply pressure on the central incisor roots causing their crowns to tip laterally Following eruption of the lateral incisors, this same effect can shift distally, and consequently the canine crowns can now compress the lateral incisor roots Although there are multiple reasons for the presence of midline dia-stema, in the early mixed dentition, this phenomenon can be part of normal physi-ological development, and midline spaces up to around two millimetres can easily resolve spontaneously following the eruption of the maxillary canines This tran-sient period of physiological spacing and flaring of the maxillary incisors is often referred as ‘ugly duckling stage’ (Fig 1.7).

Fig 1.7 Radiographic view of the ‘ugly duckling stage’ Following their eruption, the upper central incisors can be flared due to unerupted upper lateral incisors causing pressure on the distal

surface of the central incisor roots (a) After eruption of the lateral incisors, this same effect can

move distally, resulting in high upper canines now causing distal angulation of the upper lateral

incisor crowns and spacing (b)

Fig 1.6 Complete early mixed dentition Class I early mixed dentition with very mild crowding

in the lower labial segment in a 9-year-old boy Deciduous dentition has thinner enamel and in the

presence of acidic diet is more prone for erosion than permanent dentition (a–d)

a b

Fig 1.8 Occlusal features of the early mixed dentition Up to 6 mm spacing in the deciduous dentition is required to provide enough space for larger permanent teeth Developing anterior open bite present in this 3-year-old child with no family history of anterior open bite is likely to be

caused by a prolonged dummy-sucking habit (a) Midline diastema and deep bite can be transient

physiological features of the mixed dentition Permanent central incisor is approximately 2 mm

wider than deciduous central incisor (b) Permanent teeth develop lingually in relation to their

permanent successors, and occasionally, especially in the crowded dentition, lower incisors can

erupt ectopically in the side of the tongue (c, d)

Permanent incisors are visibly larger and develop on the lingual/palatal side in relation to their deciduous predecessors In the lower arch, four permanent incisors can take around six millimetres more space than the deciduous incisors This space

is obtained in variable ways such as by utilising the deciduous incisor spacing and permanent incisors erupting in more proclined inclination establishing a wider den-tal arch Even the intercanine and molar widths are essentially already established

at the age of 8 years; a small increase in the intercanine distance takes place at the time when the canines erupt [16] In the mandible approximately 1 mm increase is obtained as the lower canines erupt taking up the primate spaces available distal to the lower deciduous canines In contrast, in the maxilla lateral incisors take up the primate spaces that are present in the maxillary arch mesial to the deciduous canines However, approximately 3 mm increase is gained partially because the maxillary canines erupt in more buccal positions in comparison to their deciduous predeces-sors Lack of spacing between deciduous incisors is a strong predictor of future incisor crowding in the permanent dentition Up to 6 mm space is required to reduce the risk of developing incisor crowding [22] In the presence of crowding or retained deciduous incisors, the permanent incisors can erupt lingually/palatally due to their developmental position warranting removal of the retained deciduous teeth or inter-ceptive orthodontic treatment if maxillary incisors erupt in crossbite (Fig 1.8)

The Late Mixed Dentition (10–13 Years) (Fig 1.9 )

Eruption of the mandibular canines (9–11 years) marks the transition to late mixed dentition that happens around the same time as the start of the adolescent growth spurt Lower canines erupt more buccally and distally than their predecessors that can result in increase in the mandibular intercanine width and provide small amount

of additional space for lower incisors

First mandibular premolars erupt almost at the same time (10–12 years) with the maxillary first premolars (10–11 years) At around 11–12 years of age, the maxillary canines (11–12 years) and all four second premolars (maxillary 10–12 years and man-dibular 11–13 years) erupt This is followed by eruption of the all four second molars around the age of 11–13 years in the mandible and 12–13 years in the maxilla that com-pletes the late mixed dentition stage [12] However, dental development still continues

as formation of the third molars is now underway and undergoing crown calcification that is normally radiographically evident Also, root development of the permanent teeth

is not completed until around 2–3 years after their eruption [12] (Table 1.2)

Maxillary canine crown development is started at around 4 months of embryonic development, and root development is not completed until the age of around 13½ years They also have a long eruption pathway that is guided by the lateral incisor roots [23] In contrast to other successional teeth, maxillary canines erupt later than teeth immediately distal to them, making them more prone for localised crowding, and subsequently they often erupt in buccally displaced positions These factors together with familial tendency [24] can all contribute to the fact that around 2% of the maxillary canines are impacted [25] Majority of the unerupted canines are displaced palatally (61%) but can also be impacted aligned with the dental arch (34%) or in the buccal position (4.5%) [26] If the maxillary canines are not palpable buccally at 10 years of age, it can be indicative of them being palatally ectopic Early diagnosis of the palatally positioned maxillary canines can be beneficial as removal of the deciduous canines at the right time can sometimes normalise the eruption pathway of the maxil-lary canines depending on the severity of their displacement [27]

Fig 1.9 Asymmetric dental development Over 6 months delayed eruption of the contralateral tooth can be a sign of abnormal dental development or pathology Normal dental development and

symmetric eruption of the maxillary canines taking place in a 12-year-old boy (a) and delayed

eruption of the upper right lateral incisor at the same time with upper canines seen in a same-age cousin whose father has a peg-shaped upper lateral incisor, that is, a dental feature with strong

inheritance pattern (b)

Table 1.2 Permanent dentition: calcification of the crown begins and completed, eruption times and completion of root formation

Arch and tooth Calcification begins

Crown completed (years)

Eruption (years)

Root completed (years)

Mx Ci 3–4 months (in utero) 4–5 7–8 9–10

Mx third molar 7–9 years (after birth) 13 a 17–30 18–25 a

Md Ci 3–4 months (in utero) 4–5 6–7 9–10

Md Li 3–4 months (in utero) 4–5 7–8 10

Md canine 4–5 months (after

Md third molar 8–10 years (after birth) 13.5 a 17–30 18–15 a

According to Logan and Kronfeld [ 12 ]

a Based on data of Nyström [ 19 ]

Space and Occlusal Development in the Late Mixed Dentition

(Box 1.3)

In contrast to incisors, the total mesiodistal width of the permanent canine and two premolars occupy less space than their deciduous predecessors This space accounts for up to 2.5 mm space in the mandible and 1.5 mm in the maxilla and is called

‘leeway space’ Majority of the leeway space is provided by wide deciduous second molars, and subsequently most of this space is used by first molars that following the loss of the second deciduous molars rapidly move mesially Significantly, lee-way space also contributes to formation of the Class I molar relationship as more space for mesial migration of the molars is available in the mandibular arch than in the maxilla [28] Therefore, even the flush end of the first molars is the most com-mon relationship in the early mixed dentition, the differential mesial movement as well as faster growth of the mandible in comparison to maxilla contributes all together for 3–4 mm more mesial movement of the mandibular than the maxillary

molar, contributing to the establishment of Class I molar relationship Similarly, if Class II molar relationship is found in the deciduous dentition, this is likely to improve and Class III is likely to get worse around the time when a child shifts from the deciduous to permanent dentition Mainly because of the loss of the leeway space and mesial movement of the molars, the arch perimeter reduces during the transition to the permanent dentition approximately 3.5 mm in boys and 4.5 mm in girls [29] (Table 1.3; Fig 1.10).

Table 1.3 Mesiodistal widths of the deciduous and permanent teeth

Deciduous mesiodistal width

combined value for girls and

boys (mm)

Permanent mesiodistal width girls (mm)

Permanent mesiodistal width boys (mm)

According to Lysell and Myrberg [ 30 ]

Box 1.3 Features Ensuring Adequate Space for Permanent Dentition

– Transverse and anterior-posterior growth of the jaws

– Incisor spacing in the primary dentition

– Primate spaces in the maxilla mesial and in the mandible distal to ous canines

decidu-– Leeway space 1.5 mm in the maxilla and 2.5 mm in the mandible

– Incisors erupt into more proclined positions than upright deciduous incisors

a b

Fig 1.10 Establishing Class I molar relationship Deciduous molars are wider (a) than their cessor premolars (b) In addition, the mandibular first and second deciduous molars are wider than

suc-the maxillary deciduous molars contributing to suc-the flush vertical relationship of suc-the distal ends of

the deciduous second molars (a) This allows more mesial movement of the lower than upper

permanent first molars at the time when deciduous teeth exfoliate subsequently facilitating to the

development of Class I molar relationship (b)

Permanent Dentition (13 Years Onwards) (Fig 1.11 )

Dental development continues even after eruption of the second molars Over 20%

of the population have missing third molars [31, 32], and the rest develop one to four third molars that typically start crown calcification around the age of 9 years and complete by 14 years of age Third molars erupt in on average around the age

of 19 years, but due to posterior crowding and angular orientation, they can often be delayed or impacted

Fig 1.11 Permanent dentition Full permanent Class I dentition in a 13-year-old boy (a–d)

After teeth have reached the occlusal level and completed root development, they still continue to erupt This continued eruption together with alveolar growth com-pensates the increase in the ramus and condylar height and results in further increase

in the lower anterior facial height during adolescence and adulthood [2] Late lar growth and eruption is important to bear in mind when assessing the prognosis

alveo-of the ankylosed teeth or planning the suitable time for implant placement Neither ankylosed teeth nor implants have the ability to erupt and subsequently can become infraoccluded if the ankylosis has taken place during the childhood or adolescence

or if the implants have been placed during the time of active growth

Teeth are also exposed to occlusal forces that can cause attrition occlusally and interproximally resulting in changes in occlusion Specifically, the mandibular teeth are subject to occlusal forces with an anterior force vector that together with anterior growth rotation of the mandible as well as eruption of the third molars are thought to contribute to the development of the late incisor crowding [33] Although late incisor crowding typically occurs during late teen years, it can also appear later on during adulthood [34] Eruption of the third molars has traditionally been thought to increase the anterior forces and likelihood of late incisor crowding However, multiple studies have shown that individuals who have absent lower third molars also develop late incisor crowding providing evidence that third molars are not alone responsible for late incisor crowding, but the aetiology is more likely to be multifactorial [35, 36]

Eruption Is Divided in Five Different Stages

Eruption occurs in two distinct stages consisting of pre-emergent and post-emergent eruption Post-emergent eruption can be further divided in four phases of pre- functional spurt that takes place until teeth meet the occlusal level and juvenile equilibrium, adolescent eruptive spurt and adult equilibrium that compensate for the vertical facial growth

Pre-emergent eruption begins at the time when root formation is initiated, and two coordinated but independent processes are taking place: eruptive movement of the tooth and resorption of the surrounding bone When successional teeth erupt, also root resorption of the deciduous predecessors is necessary before they can obtain their correct positions in the dental arch Interactions between the follicle and surrounding bone consisting of osteoclasts and osteoblasts stimulate resorption that clears the eruption pathway and can subsequently act as a rate-limiting factor for eruption Studies done on dogs and coincidental finding on patients who have expe-rienced trauma show that resorption of the surrounding bone occurs even after teeth have been ligated to the lower border of the mandible [37, 38] On the other hand, after removal of the root apex, teeth still have potential to erupt, providing evidence that eruptive movement does not only rely on root development [10] These studies together indicate that eruptive movement and bone resorption are two distinct mechanisms that are differentially regulated

Eruption continues even after completion of root development Indeed, after molars have reached the occlusal level, they still continue to erupt approximately

one centimetre in order to keep up with vertical facial growth Multiple nisms have been suggested to induce the post-emergent eruption Interestingly, studies using video microscope revealed that majority of the juvenile equilibrium premolar eruption took place between 6 pm and 1 am This time correlated with high release of the growth hormone rather than changes in occlusal forces Other mechanisms that have been suggested to stimulate eruption are shrinking and cross-linking of maturating collagen fibres as well as vascular pressure created by blood flow in the periodontal ligaments [38] In addition, a more recent theory sug-gests that patterns of compression and tension created by occlusal forces and medi-ated by soft tissues provide a lifting force to teeth towards the oral cavity as compression in the coronal part of the tooth causes resorption and tension in the apical end creates bone [39].

Conclusions

Understanding normal development and maturation of the dentition is essential for any dentist who treats children, and it forms the basis for appropriate diagno-sis and treatment Any considerable deviation from average dental development can be an indication of underlying pathology or malocclusion, and it is important

to be able to identify when further investigation or referral to a specialist is essary Furthermore, a thorough knowledge of dental developmental stages can help to predict the consequences of environmental influences, such as maternal

nec-or childhood illnesses and dental trauma

References

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in the embryo Dent Update 2006;33(10):582–4, 586–8, 590–1.

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of Dlx-1 and Dlx-2 genes in patterning of the murine dentition Development

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12 Logan W, Kronfeld R Development of the human jaws and surrounding structures from birth through the age of fifteen years J Am Dent Assoc 1933;20:379–427.

13 Kurek M, Zadzinska E, Sitek A, Borowska-Struginska B, Rosset I, Lorkiewicz W Prenatal factors associated with the neonatal line thickness in human deciduous incisors Homo 2015;66(3):251–63.

14 Newadkar UR, Chaudhari L, Khalekar YK Natal and neonatal teeth: terminology with diverse superstitions!! J Family Med Prim Care 2016;5(1):184–5.

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16 Bishara SE Arch width changes from 6 weeks to 45 years of age Am J Orthod Dentofacial Orthop 1997;111:401–9.

17 Mahoney P Dental fast track: prenatal enamel growth, incisor eruption, and weaning in human infants Am J Phys Anthropol 2015;156(3):407–21.

18 McIntyre GT, McIntyre GM Teething troubles? Br Dent J 2002;192:251–5.

19 Nyström M Clinical eruption of deciduous teeth in a series of Finnish children Proc Finn Dent Soc 1977;73:155–61.

20 Sillman JH Dimensional changes of the dental arches: longitudinal study from birth to 25 years Am J Orthod 1964;50:824–42.

21 Foster TD, Hamilton MC Occlusion in the primary dentition Br Dent J 1969;126:76–9.

22 Leighton BC The early signs of malocclusion Trans Eur Orthod Soc 1969;45:353–68.

23 Becker A In defense of the guidance theory of palatal canine displacement Angle Orthod 1995;65(2):95–8.

24 Peck SM, Peck L, Kataja M The palatally displaced canine as a dental anomaly of genetic origin Angle Orthod 1994;64(4):249–56.

25 Ericson S, Kurol J Radiographic assessment of maxillary canine eruption in children with clinical signs of eruption disturbance Eur J Orthod 1986;8(3):133–40.

26 Stivaros N, Mandall NA Radiographic factors affecting the management of impacted upper permanent canines J Orthod 2000;27(2):169–73.

27 Naoumova J, Kürol J, Kjellberg H Extraction of the deciduous canine as an interceptive ment in children with palatally displaced canines – part II: possible predictors of success and cut-off points for a spontaneous eruption Eur J Orthod 2015;37(2):219–29.

28 Moyers RE Handbook of orthodontics 4th ed Ann Arbour: Year book Medical Publisher;

35 Richardson ME Late lower arch crowding: facial growth or forward drift? Eur J Orthod 1979;1:219–25.

36 Zawawi KH, Melis M The role of mandibular third molars on lower anterior teeth crowding and relapse after orthodontic treatment: systematic review ScientificWorldJournal 2014;2014(615429):1–6.

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by bite forces sensed by soft tissue dental follicles: a finite element analysis PLoS One 2013;8(3):e58803.

© Springer International Publishing AG 2017

M.T Cobourne (ed.), Orthodontic Management of the Developing Dentition,

DOI 10.1007/978-3-319-54637-7_2

A.J Ireland ( * ) • R John • J.R Sandy

School of Oral and Dental Sciences, University of Bristol,

Lower Maudlin St., Bristol BS1 2LY, UK

e-mail: tony.ireland@bristol.ac.uk ; Rebecca.John@uhbristol.nhs.uk ;

Space Loss and Crowding

Anthony J Ireland, Fraser McDonald, Rebecca John,

and Jonathan R Sandy

Abstract

Crowding and spacing within the dental arches is largely under genetic control but is affected by a number of local factors This chapter describes these local factors, discusses how they can influence the development of the dentition and also describes the interceptive measures available to the orthodontist

Introduction

Orthodontists are often expected to predict, prevent and treat the effects of crowding and space loss during development of the dentition Although this may entail com-prehensive treatment, more often than not, it comprises of short, interceptive mea-sures Before describing these measures, we should first look at the aetiology of crowding and space loss

It is worth at this point perhaps asking the question “Has crowding and space loss

always been an issue in the developing dentition?” Studies on pre- industrialised sations have shown that in most instances, there is little evidence that dental crowding was present to the same extent as is seen today [1 2] This has led to the theory that early civilisations ate a more abrasive diet, which resulted in the loss of tooth tissue, not only occlusal but also interdental As a result, the mesiodistal tooth widths of the teeth were thought to gradually reduce over time, permitting all of the teeth to fit within the arches, including the third permanent molars [3 4] Therefore pre-industrialised occlu-sions were not without crowding, it was perhaps just less common

Predictors of Crowding in the Developing Dentition

As has previously been described in Chap 1, the presence of severe crowding in the deciduous dentition is relatively rare More often than not, the teeth (in particular, the incisors) are slightly spaced Indeed, it is thought the degree of crowding or spacing of the deciduous incisors can be used as a possible predictor of the likely crowding that may be initially seen in the early permanent dentition It was Leighton who suggested that if the deciduous incisors were well aligned, with no spacing or crowding, then there were more than 2 in 3 chances that the permanent incisors would be crowded [5] If the sum of the spaces was less than 3 mm, the chance of crowding was slightly better than 1 in 2, and if the sum of the spacing was between

3 and 6 mm, this improved to 1 in 5 Where the total was greater than 6 mm then there was little chance of permanent incisors being crowded Other than this, there

is little in the way of predicting crowding

Local Factors Affecting Crowding and Space Loss

Local factors that may affect crowding and subsequent space loss include:

• Early loss of deciduous teeth

• Retained deciduous teeth

• Developmental absence of teeth

• Unscheduled loss of permanent teeth

• Extra teeth (supernumerary and supplemental)

• Anomalies in tooth form (microdont and megadont)

• Anomalies in tooth position

Of all of these local factors, it is relatively easy to understand how the presence

of large, small or extra teeth will have a direct influence on the presence of spacing

or crowding What is not quite so easy to understand is the effect when teeth are lost prematurely through trauma or disease The most important factor is most probably the presence or absence of crowding If the arches are spaced, in both the mixed or permanent dentitions, then the effect of early loss on the remaining teeth within the same arch is likely to be minimal However, in the presence of crowding, the loss of

a tooth is likely to lead to drifting of the adjacent teeth towards the site of loss This space loss, in turn, can affect occlusal relationships leading to a change in the molar relationship or a shift in the dental centreline The earlier a tooth is lost, the greater the likely effect on the developing occlusion Each of these local factors will now be described in turn

Early Loss of Deciduous Teeth

The effect of early loss of deciduous teeth will, as previously described, depend largely on the underlying crowding within the permanent dentition If there is no crowding, the effect will be minimal However, in the presence of crowding, the effect will depend on which tooth is lost and the age at which this occurs In general, the more anterior the tooth loss the greater the effect on the centreline, and the more posterior the tooth loss the greater the effect on the buccal segment tooth relation-ship, usually as a result of mesial movement of the first permanent molar In order

to try to prevent a shift in the dental centreline, it is sometimes useful to extract the same tooth on the opposite side of the same arch, known as a balancing extraction

With this in mind, “Should balancing extractions always be performed?” The

loss of a deciduous incisor is not usually balanced However, whenever a deciduous canine is lost, due, for example, to resorption of its root by the permanent lateral incisor, or a first deciduous molar is lost prematurely due to caries, it is worth bal-ancing the loss This can be done either by the extraction of the opposite deciduous canine or first deciduous molar, in order to prevent a shift of the dental centreline If

a second deciduous molar is lost prematurely, the effect on the centreline is minimal and so it should not be balanced The greatest effect of early loss of the second deciduous molar is mesial drifting of the first permanent molar, which is then likely

to encroach on the space for the second premolar This often results in the premolar being squeezed out of the arch (Fig 2.1) and eventually erupting palatal to the arch

In all cases the earlier the loss of the deciduous tooth, the greater the effect it has on either the centreline or the buccal segment relationship

“Should we ever retain the space following early loss of a deciduous tooth?” In

most instances the answer is no and there are a number of reasons for this Firstly, if the deciduous tooth has been lost prematurely due to caries, then such a patient is

unlikely to be a good candidate for the long-term wear of either a fixed or removable space maintainer Secondly, as has already been mentioned, in the absence of crowd-ing, there is no need to maintain the space, and, thirdly, if there is moderate to severe crowding, extractions may be required at a later date in any case Only very occa-sionally is space maintenance the treatment option of choice, and an example would

be the enforced extraction of an ankylosed and submerging deciduous tooth, where space maintenance might obviate the need for any future orthodontic treatment In such a case the space can be maintained with a removable or a fixed space main-tainer (Fig 2.2)

“What about compensating extractions?” A compensating extraction is an

extraction of a tooth in the opposing arch, and the aim is to preserve the buccal ment relationships of the teeth In general compensating extractions in the decidu-ous dentition are less often performed than balancing extractions

seg-Fig 2.1 Panoramic radiograph showing an impacted upper second premolar following early loss

of the deciduous second molar

Fig 2.2 Fixed space

maintainer Notice how the

lower first premolar is

beginning to erupt and

there is just sufficient

space

Retained Deciduous Teeth

Deciduous teeth are not infrequently retained beyond their normal age of eruption This may be associated with the ectopic path of eruption or developmental absence

of the permanent successor or the presence of chronic infection at the deciduous tooth root apex (Fig 2.3), all of which may delay the normal process of root resorp-tion that leads to the tooth being naturally shed In some instances this failure of resorption can lead to ankylosis and the appearance of a submerging tooth In real-ity, it is not the affected deciduous tooth that is submerging What is in fact happen-ing is that with continued facial growth the adjacent teeth erupt relative to the ankylosed tooth, which then appears to submerge Submergence is most commonly seen in the deciduous molar regions and, if left unchecked, can lead to the adjacent teeth tipping over the occlusal surface of the submerging deciduous molar (Fig 2.4)

In extreme circumstances the deciduous tooth can submerge so far that it will not be visible in the mouth, only on a radiograph Not only does this make removal of the submerged tooth somewhat difficult but it can also lead to space loss, with insuffi-cient room left for the permanent successor to erupt

This begs the question “If and when should a submerging deciduous tooth be

extracted?” In reality a degree of submergence during the lifetime of a deciduous molar is a relatively common part of normal occlusal development The eventual natural loss of a deciduous tooth is a dynamic process of root resorption and repair, and provided there is more resorption than repair, the tooth may submerge a little, re-erupt and then is ultimately shed However, if there is more repair and little resorption, the tooth is likely to ankylose and continue to submerge If a permanent successor is present and the deciduous tooth is only slightly submerged, being above the contact points of the adjacent teeth and with no signs of these teeth tipping over its occlusal surface, then the deciduous tooth can be kept under observation If the tooth submerges below the contact points of the adjacent teeth and they begin tip-ping over the occlusal surface, then extraction of the deciduous tooth and space management might be required [6]

Fig 2.3 Retained upper

central deciduous incisors

preventing the eruption of

the permanent central

incisor teeth

Developmental Absence of Teeth

It is very rare that deciduous teeth are developmentally absent However, the opmental absence of permanent teeth is relatively common Excluding the third permanent molars, there are reports that it may affect between <0.1% [7] and 10.3%

devel-of children [8] The most common missing tooth, apart from the third permanent molar, is the upper second premolar, followed by the upper lateral incisor, the lower second premolar and the lower central incisor In the early permanent dentition, when it is discovered on a radiograph that a permanent tooth is developmentally absent, there are a number of possible treatment options for the retained deciduous tooth, including:

• Preservation of the deciduous tooth for as long as possible provided it is in good condition It can then be replaced when naturally shed with a prosthetic tooth There are reports of second deciduous molars being retained in the mouth until the fifth decade of life [9], which is longer than many intraoral prostheses are able to survive

• To extract the deciduous tooth in order to encourage mesial movement on tion of other, as yet unerupted permanent teeth In this way the space created by the missing tooth is either closed or reduced, eliminating or reducing the need for later orthodontic treatment or a prosthetic replacement tooth For this to work there should be some underlying crowding; otherwise the teeth may not sponta-neously drift into the primary tooth extraction space

erup-• To preserve the deciduous tooth until a later date when it can be extracted as part

of a comprehensive orthodontic treatment plan to relieve crowding, align the teeth and close the space or relocate the space prior to the provision of a defini-tive prosthetic replacement

Whichever treatment option is chosen, it is important a full orthodontic and radiographic assessment is undertaken, being mindful that in the case of apparently missing second premolars, these may not become apparent radiographically until 9 years of age [10]

Fig 2.4 Submerging

upper left second

deciduous molar Notice

how the adjacent teeth are

tipping over the

submerging tooth

Unscheduled Loss of Permanent Teeth

As with the deciduous dentition, the effect of the loss of a permanent tooth will be dependent on a number of factors:

• Presence or absence of crowding—as with the loss of a deciduous tooth, the loss

of a permanent tooth will have a greater effect within the same arch in the ence of crowding This is because crowding will promote drifting of the adjacent teeth into the extraction site

pres-• Position of the tooth within the arch—the more anterior the tooth loss, the greater

the effect on the centreline Therefore the loss of a central incisor in a crowded arch will have a profound effect on the centreline (Fig 2.5), whilst the loss of a second permanent molar will have minimal effect Conversely the loss of a pos-terior tooth will have a greater effect on the buccal segment relationship than the loss of an incisor

• Patient age—in general and in the presence of crowding, the earlier the tooth

loss, the greater the effect, as the adjacent erupted and also unerupted teeth will drift towards the extraction site Therefore the effect will be greater in the devel-oping dentition than in the mature adult dentition

• The occlusion—the angulations of the teeth adjacent to the extraction site and the

interdigitation of remaining teeth within the arch with those in the opposing arch will both have an effect on space loss Erupted teeth will more readily tip than bodily move into an extraction site Therefore, if the crown of a tooth is angu-lated away from an extraction site, it is more likely to move into the extraction site than if it is angulated towards it (Fig 2.6) The interdigitation of teeth, par-ticularly in the buccal segments, may also have an effect on space loss If the interdigitation in the buccal segments is very good, it may prevent the teeth adja-cent to an extraction site from spontaneously drifting into it and closing the space Indeed, such interdigitation can be sufficiently effective in this regard as

to sometimes make space closure even with fixed appliances more difficult

Fig 2.5 Loss of the upper

left central incisor tooth has

resulted in space loss and a

shift of the upper centreline

to the left

Previously we have described the various treatment options available when a permanent tooth is found to be developmentally absent during the developing denti-tion, including timely deciduous tooth extractions to encourage spontaneous space closure When a permanent tooth is lost due to disease, e.g caries or periodontal disease, the treatment options are often fewer and include either the maintenance of space for a prosthetic replacement or space closure as part of a more comprehensive orthodontic treatment plan involving usually fixed appliance The treatment choice will depend on various factors including the presence of crowding and type of mal-occlusion, the skeletal pattern, overjet, overbite and buccal segment relationships

At this point it is worth perhaps considering the unscheduled loss of each permanent tooth in turn during the developing dentition:

Central incisor—the loss of a permanent central incisor due to trauma or caries can result in rapid space loss (Fig 2.7) As a result, in the upper arch, it is usually worth fitting a space maintainer, not only from the point of view of the

Fig 2.6 Notice how the

permanent canine is

mesially angulated in this

crowded case Loss of the

first premolar during the

eruption of the canine

would have encouraged the

canine to tip back into the

extraction space

Fig 2.7 Loss of the

upper left central incisor in

this crowded case has led

to complete space loss as a

result of drifting of the

adjacent teeth

immediate aesthetic improvement for the patient but also because orthodontic space closure and restoration of the lateral incisor to simulate the central incisor rarely gives a good long-term aesthetic result In the lower arch the loss of a central incisor in the presence of crowding can be incorporated into an overall orthodontic treatment plan at a later date, and in most instances space should not

be preserved whilst awaiting the development of the remaining occlusion This is because it can lead to alveolar bone loss which can make later space closure more challenging

Lateral incisor—when an upper lateral incisor is lost due to trauma or caries, once again the decision should be made whether to preserve the space or close the space If the lateral incisor is lost prior to the eruption of the upper permanent canine, it is likely the canine will erupt into the upper lateral incisor position (Fig 2.8) In which case the decision whether to close or reopen the space can only be made once the canine has erupted This decision will depend on other features of the occlusion but principally the degree of crowding/spacing and also the shape and colour of the permanent canine as a possible substitute for the lateral incisor Once again in the lower arch in the developing dentition, the loss

of a lower permanent lateral incisor is usually accepted and the occlusion treated

on its merits in the permanent dentition

Permanent canine—the permanent canine is rarely lost due to trauma or caries but

is more commonly absent due to an ectopic path of eruption This will be dealt with in Chap 7

Premolars and molars—when a first premolar tooth is lost, usually due to caries, this can lead to spontaneous space closure and unwanted affects such as a shift in the centreline or buccal segment relationship As a result when there is the enforced loss of a first premolar in a crowded arch, consideration should be given

to the loss of the first premolar on the opposite side of the same arch, a balancing extraction If the buccal segment relationship is to be preserved, then sometimes

Fig 2.8 The absence of

the upper lateral incisors in

this crowded case has led

to space loss with mesial

eruption of the upper

permanent canines

a compensating extraction is also required However, such balancing and pensating extractions may not be necessary if a space maintainer is fitted to allow, for example, a crowded upper permanent canine to drop into the line of the arch In the case of second premolars and first permanent molars in the develop-ing dentition, it is not necessary to carry out a balancing extraction to preserve centrelines, but a compensating extraction may be required to once again pre-serve the anteroposterior buccal segment relationship Other factors that will effect whether or not to compensate the loss of a first permanent molar include the presence of second and third permanent molars and whether or not the unop-posed molar tooth is likely to overerupt If all of the other molars are developing normally, then consideration should be given to the compensating extraction of the unopposed molar Not only will this reduce the likelihood of trauma from biting on the gingivae, but it will also improve the likelihood the second molar will move into the correct anteroposterior position without hindrance from an overupted first molar in the opposing arch.

Extra Teeth: Supernumerary and Supplemental Teeth

The extra teeth that most commonly disrupt the normal development of the tion include the upper midline conical supernumerary tooth or mesiodens and the tuberculate supernumerary The mesiodens can displace the path of eruption of the upper central incisors and lead to the development of a midline diastema, in which case it should be extracted The mesiodens itself may or may not erupt and is obvi-ously easy to remove if it does so (Fig 2.9) The tuberculate supernumerary usually prevents the eruption of the central incisor tooth, as it lies directly over the cingulum

denti-of the tooth Neither the supernumerary nor the central incisor will erupt As a result the supernumerary tooth should be extracted, and the central incisor may then erupt

Fig 2.9 This erupted

mesiodens has displaced

the upper central

incisors from their

normal path of eruption

spontaneously If it doesn’t it may then require exposure and bonding to bring it into the line of the arch [11] Occasionally additional teeth of similar form to the normal series develop and may erupt into the arch, and these are known as supplemental teeth Sometimes there is sufficient space to accommodate such a tooth within what would otherwise be a spaced dentition However, in most cases it leads to localised crowding, in which case a decision has to be made as to the best tooth to remove, the supplemental or the one of the normal series Sometimes it can be very difficult

to tell which is the supplemental tooth, and the extraction decision will be dent on factors such as the condition of the tooth/teeth, the position within the arch and which extraction will promote the best spontaneous improvement in the align-ment of the remaining teeth

Anomalies in Tooth Form (Microdont/Megadont)

Large or small teeth within the arch can lead to either crowding or spacing and where they are very obviously of a different size to the normal series Extraction may be the best option The decision whether or not to maintain or perhaps recreate some of the space will be dependent on the position of the tooth in question (see section “Unscheduled Loss of Permanent Teeth”) and other features of the malocclusion

Anomalies in Tooth Position

The most common ectopically positioned teeth are the permanent upper central incisor and the maxillary permanent canine The sequelae and management will be described in Chaps 7 and 8

5 Leighton BC The early signs of malocclusion Trans Eur Orthod Soc 1969;45:353–65.

6 Kennedy DB Treatment strategies for ankylosed primary molars Eur Arch Paediatr Dent 2009;10:201–10.

7 Byrd ED Incidence of supernumerary and congenitally missing teeth J Dent Child 1943;10:84–6.

8 Hunstadbraten K Hypodontia in the permanent dentition J Dent Child 1973;40:115–7.

9 Sletten DW, Smith BM, Southard KA, Casko JS, Southard TE Retained deciduous mandibular molars in adults: a radiographic study of long-term changes Am J Orthod Dentofacial Orthop 2003;124:625–30.

10 Houston WJB, Stephens CD, Tulley WJ A textbook of orthodontics Oxford: Wright; 1993.

11 Yaqoob O, O’Neill J, Gregg T, Noar J, Cobourne MT, Morris D Management of unerupted maxillary incisors 2010 https://www.rcseng.ac.uk/fds/publications-clinical guidelines/clini- cal_guidelines/documents/ManMaxIncisors2010.pdf Accessed 08/09/15.

© Springer International Publishing AG 2017

M.T Cobourne (ed.), Orthodontic Management of the Developing Dentition,

A structured assessment includes consideration of patient compliance with dental treatment, prognosis of the teeth, presence or absence of crowding and the underlying skeletal pattern

Advice provided regarding the timing of the extraction of first permanent molars will reflect any future need for orthodontic treatment, and the impact first permanent molar extractions will have on the anchorage management during future orthodontic treatment

Normal Development of the First Permanent Molar

Development of the First Permanent Molars

The first permanent molar (FPM) is rarely absent from the dentition, and when they

do fail to develop, this is usually associated with severe hypodontia Along with the upper central incisors, FPMs have been reported as the teeth least likely to be devel-opmentally absent [1] Morphological evidence of the formation of FPMs is usually present at 17 weeks in utero, and calcification of the crown commences at birth [2]

FPMs usually erupt into the mouth at the age of 6–7 years, and root formation is completed by the age of 9–10 years [3 4] The mandibular FPMs will typically erupt into the oral cavity before the maxillary FPMs As these teeth erupt, they are guided into a position in the arch that is distal to and in contact with the distal aspect

of the second primary molar

Ideal Occlusion

FPMs erupt as root formation progresses until contact is made with an opposing tooth, and the opposing tooth will typically be the FPM in the opposing arch, but some contact with primary teeth is also possible The relationship between upper and lower FPMs forms the basis of the occlusal classifications described by Edward Angle and Lawrence Andrews In the developing dentition of patients with an underlying class I skeletal base,

it is typical for the FPMs to occlude in a one-half unit class II molar relationship, with the FPMs having ‘flush terminal planes’

As the second primary molars exfoliate, there is an increased potential for the mandibular FPM to migrate mesially, and this allows for a class I molar relationship

Table 3.1 Average dimensions of FPMs

Crown height (mm)

Length of root (mm)

Mesiodistal crown diameter (mm)

Labiolingual crown diameter (mm) Maxillary FPM 7.5 12.5 10.5 11.0

Mandibular FPM 7.5 14.0 11.0 10.0

four FPMs and is frequently associated with affected incisors The severity of the extent

of the hypomineralisation can vary significantly between patients and between teeth in

an individual mouth The affected molar teeth may present with a small alised area, or more severely affected teeth may have complete breakdown of the occlu-sal surface of the tooth The destruction of the crown of affected teeth can commence during the eruption process, and patients can initially present complaining of sensitiv-ity that further impairs effective toothbrushing around the erupting teeth

hypominer-Management of FPMs presenting with a mild degree of hypomineralisation can range from the use of desensitising agents, such as the repeated application of fluo-ride varnish and the daily use of 0.4% stannous fluoride gel, to the restoration of the localised defects with adhesive restorations such as composite FPMs that are more significantly compromised and presenting with a greater extent of enamel hypomin-eralisation can be either restored with occlusal coverage restorations, such as a cast adhesive coping or a preformed stainless steel crown FPMs that are severely affected can be considered as unrestorable and require extraction

Assessing the prognosis of FPMs affected by MIH can be difficult The early presentation of affected teeth can allow for good-quality, relatively small restorations

to be placed in young patients However, if the quality of the enamel adjacent to the restoration margins is affected, the progressive breakdown of the enamel of the tooth can be difficult to prevent over time, meaning the prognosis of the tooth is inherently compromised Similarly, the option of temporising FPMs affected by MIH, to allow for the teeth to be extracted at a later stage in development, can also be compromised

by the affected teeth being symptomatic and difficult to restore (Fig 3.1)

Fig 3.1 A 9-year-old girl presented with MIH and FPMs of poor prognosis The upper left panel

shows the DPT taken at age 9, which resulted in a decision being made to extract all four FPMs The remaining panels show the same patient as a young adult with composite restorations on the anterior teeth and favourable space closure in the buccal segments without the need for orthodontic treatment